1. Field of the Invention
The present invention relates to a water dispersible, modified polyurethane, a thickened aqueous composition containing the modified polyurethane, and a method of increasing the high shear viscosity of an aqueous composition by incorporating the modified polyurethane. The present invention also relates to a method of preparing the modified polyurethane.
2. Description of the Prior Art
It has long been known in the art to use various materials to thicken an aqueous system. Depending on the composition of the aqueous system, the gels produced with these thickeners are useful as decorative and protective coatings, paper coatings, cosmetics and personal care items, adhesives and sealants, inks, petroleum drilling fluids, packer fluids, and the like.
The thickener serves several roles in aqueous systems. In the latex decorative coatings, for instance, the thickener may provide improved stability and pigment suspension, and improved application properties. In cosmetics and personal care items, the thickener will improve body, smoothness and silkiness, thereby making the product more aesthetically pleasing. In petroleum drilling fluids, the thickener improves the suspension of the cuttings, thereby increasing the efficiency with which they can be removed.
Many thickeners, both natural and synthetic, are known in the art. However, all suffer from some disadvantage that limits their usage. Natural thickeners, for instance, include casein, alginates, gum tragacanth, and modified cellulose, including methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and carbomethoxy cellulose. These natural products vary in their thickening efficiency, and provide poor flow and leveling properties. Further, they are subject to microbial attack which requires the additional presence of antimicrobial agents.
Synthetic thickeners include various acrylic polymers and maleic anhydride copolymers. Some of these are found to be pH dependent, others are hydrolytically unstable, and others are sensitive to various components normally found in aqueous coatings.
One type of synthetic thickener is a low molecular weight polyurethane characterized by at least three hydrophobic groups interconnected by hydrophilic polyether groups as disclosed in U.S. Pat. Nos. 4,079,028 and 4,155,892. The polyurethane is prepared by reacting at least one water soluble polyether polyol with at least one monofunctional hydrophobic organic compound selected from monofunctional active hydrogen compounds and organic monoisocyanates. The hydrophilic polyether group can be derived from a polyoxyalkylene diol, an adduct of an alkylene oxide and a monofunctional or difunctional reactant or an amino-terminated polyoxyethylene. There may also be present in the reaction mixture at least one water insoluble organic polyisocyanate or at least one polyhydric alcohol or polyhydric alcohol ether.
A mixture of the polyurethane described in U.S. Pat. Nos. 4,079,028 and 4,155,892 and a liquid emulsion polymer made from an addition polymerizable acid, an addition polymerizable nonionic vinyl monomer, and a nonionic vinyl surfactant ester is set forth in U.S. Pat. No. 4,507,426. The use of a related polyurethane in combination with a surfactant co-thickener and a non-aqueous, inert organic diluent to thicken print paste is set forth in U.S. Pat. No. 4,180,491.
Another type of urethane rheology modifying agent which is useful in water and organic solvent based compositions is disclosed in U.S. Pat. No. 4,298,511. The rheology modifier is the reaction product of a polyalkylene oxide, a polyfunctional material having at least 3 active hydrogens or at least 3 isocyanate groups, a diisocyanate and water. The reactants are selected such that there are no terminal hydrophobic groups in the rheology modifying agent.
A urethane thixotropic agent for coating compositions is set forth in U.S. Pat. No. 4,314,924. The thixotropic agent is prepared by reacting a mono-hydroxy compound with a diisocyanate to form mono-isocyanate adduct. The adduct is then converted into a urea-urethane by reaction with a polyamine in an aprotic solvent in the presence of lithium chloride.
In U.S. Pat. No. 3,923,926, a thixotropic polyurethane is prepared by reacting a polyurethane prepolymer having at least two terminal free isocyanate groups and a block polyether compound formed from ethylene oxide and propylene oxide and having at least two terminal secondary alcohol groups. To enhance the thixotropic property, finely divided silica or bentonite may be added.
In order to render the polyurethane insoluble in water and other types of solvents, diamines, dicarboxylic acids and other materials have been used as crosslinking agents. Illustrative of the art disclosing the use of crosslinking agents are J. M. Buist and H. Gudgeon's "Advances in Polyurethane Technology", pages 49 ff, the "Encyclopedia of Polymer Science and Technology", Volume II, pp. 55 ff and 527 and Bernard A. Dunbrow's "Polyurethanes, Second Edition", p. 28.
A further example of a crosslinked polyurethane is disclosed in U.S. Pat. No. 4,293,679. In that patent, solid, discrete, hydrophilic, crosslinked polyurethane particles are formed from a composition which comprises: a) a water reactant; b) a defined isocyanate capped prepolymer; c) a water soluble solvent for b); and d) when the reaction functionality of b) is two, a crosslinking agent containing at least three functional groups.
A different type of crosslinked polyester-urethane is described in U.S. Pat. No. 3,804,810. The polymer is prepared by reacting a) a defined linear polyester, b) at least one organic diisocyanate, and c) at least one crosslinking agent having a functionality greater than 2. The crosslinked polyester-urethane is stated as being useful in adhesives, coating compositions, primers, and for binding magnetic and/or conductive particles to a suitable support.
In U.S. Pat. No. 4,499,233, a water dispersible modified polyurethane is described. The modifying agent has the general formula X.sub.x --R--Y.sub.y wherein R represents a group containing from 0 to 10 carbon atoms, X is a group containing at least one active hydrogen moiety selected from the group consisting of primary amino, secondary amino, carboxyl and mixtures thereof, Y is a group containing at least one active hydrogen moiety selected from the group consisting of primary amino, secondary amino, carboxyl, hydroxyl, mercapto and mixtures thereof, the sum of (x+y) is an integer greater than 1 and x is at least 1. Examples of the polyurethane modifying agent are hydrazine, .alpha.,.omega.-amino alkanes, such as 3-cocoamino-1-propylamine, 3-tallowamino-1-propylamine, 3-(hydrogenated tallow)amino-1-propylamine, and N-alkyl-N,N bis(3-aminopropyl) amine, wherein the alkyl group contains one to 22 carbon atoms, dicarboxylic acids, .alpha.-amino acids, .alpha.-amino-.omega.-carboxylic acids, hydroxylamines, hydroxy acids, mercaptoamines and mixtures thereof. The disclosed preferred modifying agents are ethylene diamine, 1,6-diaminohexane, 1,10-diaminodecane, N-phenyl-p-phenylenediamine, succinic acid, suberic acid, sebacic acid, 1,10-decanedicarboxylic acid, ethanolamine, 2-(ethylamino)ethanol, and p-carboxy-phenol and mixtures thereof and the disclosed most preferred modifying agent is ethylene diamine. In U.S. Pat. No. 4,436,862, a thermally stable thickener comprised of a defined smectite-type clay and the water dispersible modified polyurethane is set forth.
U.S. Pat. No. 4,496,708 discloses a water-soluble polyurethane comb polymer which is used to thicken aqueous systems. The polyurethane has a hydrophilic polyether backbone and pendant monovalent hydrophobic groups of sufficient size and number while establishing a proper hydrophilic/lipophilic balance. The hydrophobic groups are separated from each end of the polymer by at least one hydrophilic polyether unit. Also see U.S. Pat. No. 4,426,485.
Despite the activity in the art, there has not been produced a water dispersible, modified polyurethane which is useful for increasing the high shear viscosity of an aqueous composition in an efficient manner while still attaining acceptable levels of other important characteristics.